Device and method for holding a metal sheet on a rim of a mold tool and system

ABSTRACT

A device for holding a metal sheet on a rim of a mold tool, the rim surrounding a female mold in the mold tool. The device comprises: a flexible conduit comprising a fluid; a pressure applicator configured to provide a pressure to the fluid in the flexible conduit; a contact surface configured to contact the metal sheet opposite to the rim. The flexible conduit is configured to transmit the pressure in the fluid to the contact surface such that the contact surface provides a holding force to the metal sheet on the rim of the mold tool, wherein the holding force is equal on each position of the contact surface.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the German patent application No. 102018114340.0 filed on Jun. 15, 2018, the entire disclosures of which are incorporated herein by way of reference.

FIELD OF THE INVENTION

The invention relates to a device and a method for holding a metal sheet on a rim of a mold tool and a system comprising the device.

BACKGROUND OF THE INVENTION

Sheet metal forming using a female mold may create compressive stress at the sheet edges, which may lead to buckling. Clamping of the sheet is used to prevent buckling and to reduce compressive stresses at the buckling sensitive edges. However, the clamping of the edges results in higher tensile stresses in further areas of the metal sheet.

Clamping is usually performed using a precise blank holder for the metal sheet and a significant amount of screws, e.g., greater than 100 screws for forming a rear pressure bulkhead. A uniform pressure distribution is required to prevent local effects on the sheet edges such as buckling. That clamping procedure results in high costs and workload. Furthermore, high costs are generated by the clamping system due to its very tight manufacturing tolerances.

Thus, there is the need for providing a device and a method which avoid buckling on the edges of the metal sheet while providing reduced costs and workload.

SUMMARY OF THE INVENTION

According to the invention, a device for holding a metal sheet on a rim of a mold tool is provided, the rim surrounding a female mold in the mold tool, the device comprising: a flexible conduit comprising a fluid; a pressure applicator being configured to provide a pressure to the fluid in the flexible conduit; a contact surface being configured to contact the metal sheet opposite to the rim; wherein the flexible conduit is configured to transmit the pressure in the fluid to the contact surface such that the contact surface provides a holding force to the metal sheet on the rim of the mold tool, wherein the holding force is equal on each position of the contact surface.

The present invention uses hydrostatic pressure generated in the flexible conduit to transform heterogeneous loads into a homogeneous clamping pressure. Prior to the provisioning of the pressure in the flexible conduit, the device is arranged on a metal sheet which is positioned on the mold tool having a female mold. The metal sheet will be formed into the female mold. Therefore, prior to the molding process, the metal sheet contacts the mold tool on the rim of the female mold. The contact surface of the device is arranged opposite to the rim on the metal sheet. When pressure is applied to the fluid in the flexible conduit by the pressure applicator, the flexible conduit transmits the pressure in the fluid to the contact surface such that the contact surface is pressed on the metal sheet. This results in the clamping force which presses the metal sheet on the rim of the mold tool. Since the fluid in the flexible conduit distributes any pressure that is locally provided to the flexible conduit, the pressure is distributed homogeneously to the contact surface such that the holding force is equal on each position of the contact surface. This means that the holding force will be the same when measuring the force at any point on the contact surface. This results in a very homogeneous force distribution for the clamping of the metal sheet. Buckling may be prevented due to the homogeneous force distribution. Furthermore, the tolerance requirements of the components of the device may be reduced due to the use of the flexible conduit which significantly reduces tooling costs.

In an example, the flexible conduit may also be a flexible tube or a hose.

In an example, the pressure being applied by the pressure applicator may be adjustable. Then, the adjustable pressure is transmitted to the contact surface.

In an example, the device comprises a channel comprising a first wall and a second wall, wherein the first wall and the second wall are configured to be arranged on the metal sheet opposite to the rim, wherein the flexible conduit is arranged in the channel between the first wall and the second wall.

The first wall and a second wall of the channel provide a barrier for the flexible conduit which holds the flexible conduit at its position when pressure is applied to the fluid inside the flexible conduit. A deformation of the flexible conduit which is not directed to the contact surface is prevented by the first wall and the second wall. This simplifies the handling of the device.

In an example, the channel is arranged in a U-shaped profile. U-shaped profiles are low cost components which may be easily adapted to the shape of the rim of the mold tool. Thus, due to the easy adaptation of the U-shaped profiles, the channel may be adapted to the shape of the rim of the mold tool such that the shape of the flexible conduit and the shape of the contact surface may be correspondingly adapted to the shape of the rim. This reduces the manufacturing costs of the device and provides for an easy handling of the device.

In an example, the U-shaped profile comprises the contact surface. This means that the U-shaped profile may be directly arranged on the metal sheet opposite to the rim of the mold by arranging the contact surface on the metal sheet. The flexible conduit and the channel of the U-shaped profile then presses the U-shaped profile on the metal sheet by transmitting the pressure being applied to the fluid in the flexible conduit to the U-shaped profile and thus to the contact surface. This simplifies the handling of the device and provides a stable arrangement of the device on the metal sheet.

In an example, the flexible conduit comprises the contact surface. In that exemplary embodiment, the flexible conduit is directly arranged on the metal sheet with the contact surface. Any pressure being applied to the fluid in the flexible conduit will be transmitted to the contact surface resulting in a clamping force which presses the metal sheet to the rim of the female mold. This reduces the manufacturing costs of the tool and provides a simple arrangement of the device on the metal sheet.

In an example, the pressure applicator comprises an adjustable clamp being configured to provide pressure to the fluid in the flexible conduit. The adjustability of the clamp results in an adjusting clamping force being provided to the fluid in the flexible conduit. Hence, the pressure in the fluid may be adjusted by the adjustable clamp. This results in an adjustable clamping force being provided at the contact surface. This increases the flexibility of the device since the clamping force of the device may be adjusted to the properties of the metal sheet and the requirements of the mold tool and the molding process.

In an example, the pressure applicator comprises an applicator body being arranged in contact with the flexible conduit and being configured to press the flexible conduit. The applicator body may be arranged such that it presses the flexible conduit in a direction of the contact surface.

According to the invention, also a system is provided, the system comprising: a mold tool having a female mold, and a rim surrounding the female mold; at least one fixation element; and a device according to the description above; wherein the at least one fixation element connects the device to the mold tool.

The device may be connected to the mold tool using the fixation element. The metal sheet may then be arranged in between the device and the mold tool. The fixation element provides a fixed connection between the mold tool and the device such that the device will hold its position on the metal sheet after the fixation. This simplifies the handling of the device. Furthermore, the application of pressure by the pressure applicator may be simplified.

The effects and further embodiments of the system according to the present invention are analogous to the effects and embodiments of the description mentioned above. Thus, it is referred to the above description of the device.

In an example, the fixation element comprises at least one non-adjustable clamp. The use of the non-adjustable clamp provides a fast clamping process on at least one fixation position. In combination with the embodiment of the pressure applicator having an adjustable clamp, the non-adjustable clamp simplifies the fixation and the handling of the device since the pressure may be adjusted by adjusting the adjustable clamp. Then, a change of the clamping force of the fixation element is not required.

In an example, the mold tool is a creep-forming mold tool comprising at least one air outlet opening in the female mold, wherein the air outlet opening is connected to a suction device. When using the creep-forming mold tool for the manufacturing of components which are made by welding together at least two metal sheets, the adjustable homogeneous clamping force provides a simplification of the manufacturing process of those components. Due to the homogeneous clamping force being provided by the device, the weld seam of the two metal sheets will not be subject to high stresses. Due to the low stress on the weld seams, the number of the weldings may be reduced, which means that bigger metal sheets may be used for reducing those components. This reduces the number of process steps, which simplifies the manufacturing and reduces costs.

In an example, the female mold is a mold for a pressure bulkhead.

In another example, the female mold is a mold for a shell of a fuselage.

According to the invention, also a method for holding a metal sheet on a rim of a mold tool is provided, the rim surrounding a female mold in the mold tool, the method comprising the following steps: a) Arranging a metal sheet on a rim of a mold tool, the rim surrounding a female mold of the mold tool; b) Arranging a contact surface of a device as described above opposite to the rim on the metal sheet: c) Providing pressure to the fluid of the device to hold the metal sheet on the rim with the pressure applicator of the device.

In an example, step b) comprises the sub-step: b1) Fixing the device to the mold tool.

The effects and further embodiments of the method according to the present invention are analogous to the effects and embodiments of the description mentioned above.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is described by the means of an exemplary embodiment using the attached drawing.

FIG. 1 shows a schematic drawing with a cross-sectional view of the system and the device.

FIGS. 2a-c show schematic drawings of different embodiments of the device.

FIGS. 3a-c show schematic drawings of different embodiments of the system.

FIG. 4 shows a schematic flowchart of the method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The system is labelled with the reference sign 10 in its entirety, as shown in FIG. 1.

The system 10 comprises a mold tool 12 having a female mold 14 being encircled by a rim 18, and a device 20 for holding a metal sheet 16 on the rim 18 of the mold tool 12.

In the example of FIG. 1, the metal sheet 16 is arranged between the mold tool 12 and the device 20. The device 20 comprises a pressure applicator 24, a flexible conduit 26 and a contact surface 38.

The flexible conduit 26 is filled with a fluid 28. When the device 20 is mounted for holding the metal sheet 16 on the mold tool 12, the contact surface 38 is in contact with the metal sheet 16, i.e., the contact surface 38 is arranged opposite to the rim 18. The flexible conduit 26 is arranged between the pressure applicator 24 and contact surface 38.

The pressure applicator 24 is configured to apply pressure to the flexible conduit 26. This provides pressure to the fluid 28. Due to the pressure in the fluid 28, the flexible conduit 26 is pushed towards the rim 18 of the mold tool 12. This presses the metal sheet 16 to the rim 18 of the mold tool 12.

The fluid 28 in the flexible conduit 26 distributes the pressure being provided by the pressure applicator 24 evenly to the inner wall of the flexible conduit 26. Thus, a locally provided force on the flexible conduit 26 results in a pressure in the flexible conduit 26 which provides a constant force on the inner walls of the flexible conduit. This force is transmitted to the contact surface 38 such that the contact surface 38 holds the metal sheet 16 on the rim 18 with a holding force which is equal at each position on the contact surface 38.

FIGS. 2a to 2c show different exemplary embodiments of the device 20 in more detail.

FIG. 2a shows an example wherein the device 20 comprises a flexible conduit 26 that is elastic. The material of the flexible conduit 26 may, for example, be rubber. This means that the area of the wall of the flexible conduit 26 may change. The flexible conduit 26 is arranged in a channel 22 being provided by a U-shaped profile. The channel 22 is arranged between a first wall 30 and a second wall 32 which may be the walls of the U-shaped profile. Furthermore, the contact surface 38 is arranged on the U-shaped profile. This means that the U-shaped profile contacts the metal sheet 16. Furthermore, a section of the U-shaped profile comprising the contact surface 38 is arranged between the flexible conduit 26 and the metal sheet 16.

The pressure applicator 24 comprises an applicator body 34 which may be introduced into the channel 22 to provide pressure to the flexible conduit 26. The applicator body 34 has a width which may span the distance between the first wall 30 and the second wall 32. In another example, the applicator body 34 may also have a width which is slightly smaller than the distance between the first wall 30 and the second wall 32. In the latter example, the insertion of the applicator body 34 into the channel 22 is simplified.

When the applicator body 34 travels into the channel 22, the space in the channel 22 is reduced. By reducing the space in the channel 22, the applicator body 34 deforms the flexible conduit 26 being made of an elastic material. The deformation of the flexible conduit 26 will continue until the flexible conduit 26, i.e., the fluid 28, completely fills the space between the applicator body 34 and the channel 22. In this stage, every force being applied by the applicator body 34 to the flexible conduit 26 will increase the pressure that is applied to the fluid 28.

Due to the elastic features of the flexible conduit 26 of the example of FIG. 2a , the flexible conduit 26 may fill the space between the applicator body 34 and the first wall 30 or the second wall 32, respectively. Since this would reduce the force being applied towards the metal sheet 16, the device 20 further comprises filler elements 36 which close the gap between the applicator body 34 and the first wall 30 or the second wall 32, respectively.

The application of pressure by the pressure applicator 24 therefore results in a holding force at the contact surface 38. Due to the fluid 28 which distributes the pressure being applied by the pressure applicator 24, the holding force is homogeneously distributed to the contact surface 38.

FIG. 2b shows another exemplary embodiment of the device 20. In this embodiment, the flexible conduit 26 is made of an inelastic material. The material of the flexible conduit 26 may, for example, be a fabric material which is impervious for the fluid 28.

In this example, the pressure applicator 24 comprises a plunger 40 which has a height being much smaller than the distance between the first wall 30 and the second wall 32. Since the flexible conduit cannot be elastically deformed, the dimensions of the wall of the flexible conduit 26 will not change. This means that the area of the wall of the flexible conduit 26 will not change either. Therefore, if pressure is applied by the pressure applicator 24 to the fluid 28 in the flexible conduit 26, the force resulting from the pressure is immediately applied to the walls of the entire flexible conduit 26. In the beginning of the pressure application, this will change the shape of the flexible conduit 26 such that the flexible conduit 26 will contact the first wall 30 and the second wall 32.

When the flexible conduit 26 contacts the first wall 30 and the second wall 32, the pressure applicator 24 will apply pressure to the fluid 28 in the flexible conduit 26. The fluid 28 will evenly distribute the pressure to the inner walls of the flexible conduit 26. The section of the wall of the flexible conduit 26 which sandwiches the contact surface 38 with the metal sheet 16 will then transmit a homogeneous holding force to the contact surface 38.

To reduce the stress on the flexible conduit 26 while the pressure applicator 24 applies pressure to the flexible conduit 26, any edges inside the channel 22 of the U-shaped profile may be covered by covering elements 42.

FIG. 2c shows a further exemplary embodiment of the device 20. In this embodiment, the channel 22 is provided by the first wall 30, the metal sheet 16 and the second wall 32. The flexible conduit 26 is in direct contact with the metal sheet 16. Hence, the contact surface 38 is arranged on the flexible conduit 26.

The embodiment of FIG. 2c shows an example wherein the rim 18 has an annular shape. Consequently, the channel 22 has the same annular shape. This means that the first wall 30 and the second wall 32 are annular, too. When pressure is applied to the flexible conduit 26, the homogeneous distribution of the pressure by the fluid 28 in the flexible conduit 26 will hold the first wall 30 and the second wall 32 in position.

In a further example, not being shown, which is based on the embodiment of FIG. 2c , the first wall 30 and the second wall 32 are connected by connecting elements like rods or struts. This means that direct contact between the flexible conduit 26 and the metal sheet 16 may be interrupted at the positions of the connecting elements.

FIGS. 3a to 3c show top views on the system 10. Those figures show the pressure applicator 24 which is fixed on the metal sheet 16 by fixation elements 44, 48. The fixation element 44 may be a non-adjustable clamp which is connected to the mold tool 12. The non-adjustable clamp 44 presses the pressure applicator 24 in direction of the mold tool 12.

The fixation element 48 may be a hinge which is connected to the mold tool 12 and to the pressure applicator 24. The hinge 48 provides a joint between the pressure applicator 24 and the mold tool 12 such that the pressure applicator 24 may be swung open from the rim 18 of the mold tool 12.

Furthermore, the device 20 may comprise an adjustable clamp 46 which may be connected to the mold tool 12. The adjustable clamp 46 may provide an adjustable clamping force on the pressure applicator 24, the force being directed to the rim 18 via the flexible conduit 26 and the fluid 28.

Due to the fluid 28 in the flexible conduit 26 which is pressed by the pressure applicator 24, the adjustment of the clamping force with the adjustable clamp 46 will change of the pressure of the fluid 28 along the entire length of the flexible conduit 26. This means that a simple local adjustment of the clamping force with the adjustable clamp 46 is sufficient to globally change the pressure of the fluid 28.

FIG. 3a shows an annular pressure applicator 24 on a circular metal sheet 16. The circular metal sheet 16 may, for example, be arranged on a female mold 14 for a pressure bulkhead. After clamping the metal sheet 16 to the rim 18 with the device 20, the metal sheet 16 may be creep-formed into the female mold 14 to be brought into the shape of the pressure bulkhead.

The creep-forming may be provided by a suction device 52 which is connected to an opening 50 in the female mold 14.

FIG. 3b shows another exemplary embodiment comprising two devices 20. The pressure applicators 24 are linear and arranged parallel to each other on the edges of a square-shaped metal sheet 16. The square-shaped metal sheet 16 may be arranged on a female mold 14 of a shell of a fuselage.

FIG. 3c shows a further exemplary embodiment. In this example, the pressure applicator 24 has a rectangular shape. As in the example shown in FIG. 3b , the metal sheet 16 in FIG. 3c is square-shaped. This means that also the rim 18 of the female mold 14 on which the metal sheet 16 is arranged on is square-shaped.

FIG. 4 shows a flowchart of the method 100 for holding a metal sheet on a rim of a mold tool.

In a first step a) a metal sheet is arranged 101 on a rim of a mold tool. The rim surrounds a female mold of the mold tool.

In a further step b), the contact surface of the device according to the description above is arranged 102 on the metal sheet such that the contact surface is opposite to the rim.

The device may be fixed 103 to the mold tool in a step b1).

Then, pressure may be provided 104 to the fluid of the flexible conduit of the device using the pressure applicator of the device. This will hold the metal sheet on the rim. Due to the fluid in the flexible conduit of the device, the pressure is homogeneously distributed to the inner walls of the flexible conduit. This results in a pressure force which is transmitted to the contact surface. Consequently, the holding force which is present at the contact surface is homogeneous such that at every position of the contact surface the holding force is equal.

While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority. 

1. A device for holding a metal sheet on a rim of a mold tool, the rim surrounding a female mold in the mold tool, the device comprising: a flexible conduit comprising a fluid; a pressure applicator configured to provide a pressure to the fluid in the flexible conduit; a contact surface configured to contact the metal sheet opposite to the rim; wherein the flexible conduit is configured to transmit the pressure in the fluid to the contact surface such that the contact surface provides a holding force to the metal sheet on the rim of the mold tool, wherein the holding force is equal on each position of the contact surface.
 2. The device according to claim 1, wherein the device comprises a channel comprising a first wall and a second wall, wherein the first wall and the second wall are configured to be arranged on the metal sheet opposite to the rim, wherein the flexible conduit is arranged in the channel between the first wall and the second wall.
 3. The device according to claim 2, wherein the channel is arranged in a U-shaped profile.
 4. The device according to claim 3, wherein the U-shaped profile comprises the contact surface.
 5. The device according to claim 1, wherein the flexible conduit comprises the contact surface.
 6. The device according to claim 1, wherein the pressure applicator comprises an adjustable clamp being configured to provide pressure to the fluid in the flexible conduit.
 7. The device according to claim 1, wherein the pressure applicator comprises an applicator body being arranged in contact with the flexible conduit and being configured to press the flexible conduit.
 8. A system comprising: a mold tool having a female mold, and a rim surrounding the female mold; at least one fixation element; and a device according to claim 1; wherein the at least one fixation element connects the device to the mold tool.
 9. The system according to claim 8, wherein the fixation element comprises at least one non-adjustable clamp.
 10. The system according to claim 8, wherein the mold tool is a creep-forming mold tool comprising at least one opening in the female mold, wherein the opening is connected to a suction device.
 11. The system according to claim 8, wherein the female mold is a mold of a pressure bulkhead.
 12. The system according to claim 8, wherein the female mold is a mold for a shell of a fuselage.
 13. A method for holding a metal sheet on a rim of a mold tool, the rim surrounding a female mold in the mold tool, the method comprising the following steps: a) arranging a metal sheet on a rim of a mold tool, the rim surrounding a female mold of the mold tool; b) arranging a contact surface of a device according to claim 1 opposite to the rim on the metal sheet: c) providing pressure to the fluid of the device to hold the metal sheet on the rim with the pressure applicator of the device.
 14. The method according to claim 13, wherein step b) comprises the sub-step: b1) fixing the device to the mold tool. 